The use of synthetic metalloporphyrins as catalysts for liquid-phase oxidation reactions has for a number of years been the subject of numerous publications, for example those illustrated by Mc. Murry, J. T. Groves in "Cytochrome P. 450; Structure, Mechanism and Biochemistry" Plenum, New York, 1986, pp 1-28.
These publications have revealed the important part played by the proximal ligand in the control of the rate, of the chemical selectivity and of the stereochemistry of the oxidation reaction (cf. B. Meunier et al., J. Am. Chem. Soc. 106, 6668-6676; 1984). To modify the reactivity of the catalyst systems which are employed, comprising of metalloporphyrins and an oxidizing agent such as H.sub.2 O.sub.2 or peroxides, this has led the investigators to add to the reaction mixture a nitrogenous base such as pyridine or imidazole (French patent 81/23,665 of 18.12.1981), which acts as an axial ligand. However, the limitation of this method is linked with the fact that the nitrogenous base is present in excess in a highly oxidizing reaction medium, which results in an oxidation of the cocatalyst and hence in a high consumption of the nitrogenous base.
Furthermore, these oxidative processes are conducted using homogeneous catalysis, and this involves difficulties in subsequently isolating the reaction product from the reaction mixture, and also problems in recovering the catalyst and its cocatalyst with a view to reutilization.
To overcome this disadvantage it has been proposed by the Assignee herein in a pending French application No. 88/09,169 of July 1988, to work using heterogeneous catalysis with a sulfonated metalloporphyrin catalyst fixed on a support of the ion exchange resin type (Amberlite R). This solution, which is advantageous on an industrial scale, does not, however, avoid the need to add the nitrogenous base to the reaction mixture.
The objective of the present invention is oxidation catalysts which make it possible to work using heterogeneous catalysis and which, comprising the axial ligand needed for the reaction, avoid the addition of the nitrogenous base and hence its consumption during the reaction process.
The subject of the present invention is new catalysts for liquid-phase oxidation of functional organic compounds, comprising of metalloporphyrins carrying anionic groups as substituents, active in the presence of an oxidizing agent, in which the metalloporphyrin is immobolized on a support, insoluble in the liquid phase, of polymeric type comprising nitrogenous groups acting as a Lewis base. The attachment of the metalloporphyrin takes place via a covalent bond between the metal of the porphyrin and the nitrogen of the supporting polymer.
The metalloporphyrins forming part of the composition of the catalysts of the invention are all porphyrins which have an axial site which is free or which is occupied by an axial ligand which can be easily displaced by the potential coordinate. Specifically, the nitrogen of the nitrogenous group originating from the support employed and negatively charged groups (or producing such groups after ionization), which are referred to in this text by the expression anionic groups, at the periphery of the porphyrinic ligand.
The most usual anion groups in the case of the porphyrinic compounds are carboxylic acid or sulfonate functional groups.
The metalloporphyrins employed for the catalysts of the invention can be the metal complexes of porphyrins of the class of natural porphyrins containing no substituents in a meso position but at least one anionic group in the pyrrolic positions. By way of examples there may be mentioned deuteroporphyrin IX, mesoporphyrin-IX, protoporphyrin-IX, and uroporphyrins I and III.
The preferred metalloporphyrins are porphyrins which are meso-substituted by aromatic radicals. The aryl radicals themselves will carry substituents such as alkyl or aryl groups or halogens, for example chlorine, in the ortho,ortho' (2,6) positions and at least one sulfonate functional group or a carboxylic acid functional group.
The porphyrins are metallized as a function of the type of reaction used. The metal will be chosen from, for example, chromium, manganese, iron, cobalt, nickel, platinum or iridium. Iron and manganese are particularly well suited for many oxidation reactions.
By way of example of metalloporphyrins which are well suited to the catalysts of the invention there may be mentioned: Mn-TMPS and FE-TMPS; TMPS denoting 5,10,15,20-tetrakis (3,5-disulphonatomesityl)porphyrin. These porphyrins are described in a pending French patent application by the Assignee herein. There may also be mentioned: Mn-TDCPS and Fe-TDCPS, that is to say the manganese and iron derivatives of 5,10,15,20-tetrakis (3-sulphonato2,6-dichlorophenyl)porphyrin and the metal derivatives of meso-tetra(para-carboxyphenyl)porphyrin.
The support on which the metalloporphyrin will be immobolized will be a polymer or a copolymer carrying nitrogenous groups used as a Lewis base. These nitrogenous groups will result either from the copolymerization of a monomer carrying these groups or from the grafting of these groups onto a polymer. These nitrogenous groups will be preferably of the pyridine, histidine or imidazole type.
By way of examples of such polymers there may be mentioned polyvinylpyridine/divinylbenzene (2, 3, or 4-vinylpyridine/divinylbenzene) copolymers, polyvinylimidazole/divinylbenzene copolymers, polyphenylquinoxaline/divinylbenzene copolymers, poly(N-vinylcarbazole)/divinylbenzene copolymers, polyvinylpyridine/ styrene copolymers, crosslinked polyhistidines or copolymers of histidine-rich amino acids.
The immobilization of the metalloporphyrin on the support will be produced by attaching the nitrogenous groups to the metal of the metalloporphyrin by covalent bonds according to a known process.
The process of attaching by a covalent bond will comprised treating the polymers containing the nitrogenous groups used as a Lewis base with an acid leading to a cationic resin by protonation of the nitrogenous sites, in treating the said resin with a base permitting the deprotonation of these nitrogenous sites, in bringing the resin into contact with the anionic metalloporphyrin for a time which is sufficient for an attachment of covalent type and then, finally, in reprotonating with an acid the nitrogenous groups which are not involved in the covalent attachment.
The reprotonation allows the creation of bonds between the anionic groups of the porphyrin and the ammonium-type nitrogenous cations of the polymer. This makes it possible to produce a double attachment--one of covalent-bond type and the other by electrostatic interaction --of the porphyrin to the sites of the polymer, endowing the final catalyst with great stability.
These catalysts can be employed:
in oxidative processes: oxidation of alcohols, aldehydes, decarboxylation (decarboxylation of phenylacetic acid to benzoic acid), oxidation of aliphatic and aromatic amines, oxidation of sulphides and of thiols and oxidative breaking of C--C, C--N and C--O bonds,
in halogenation processes: chlorination and bromination of aliphatic and aromatic compounds (chlorination of .beta.diketones: chlorination of dimedone to chlorodimedone).
These reactions are carried out in an organic medium (dichloromethane, acetonitrile, etc.) or in an essentially aqueous medium (acetonitrile/buffered water mixture), in the presence of any suitable oxidizing agent: water-soluble organic and inorganic peracids and peroxides: H.sub.2 O.sub.2, sodium hypochlorite, KHSO.sub.5, magnesium salt of peroxyphthalic acid, or those which are soluble in an organic medium: e.g. tert-butyl hydroperoxide and cumene hydroperoxide.
The catalysts of the invention are illustrated by the examples below which relate to the preparation of the said catalysts and their use for the oxidation of benzyl alcohols: veratryl alcohol (I) and a dimer, 1-(3,4-dimethoxyphenyl)-2-(2-methoxyphenoxy)-1,3-propanediol (II).